1ft 2.5mm TRS Headset Jack to RJ9/RJ10 Cisco IP Office Phone Adapter, IP-CS12 

This 2.5mm TRS headset jack to RJ9/RJ10 plug adapter cable let you use your 2.5mm headset with Cisco office VoIP Phone.
Eliminates the need to have more than one headset. Great for home businesses, offices, call centers, and more..

Works with these Cisco VoIP Phones:
6921, 6941, 6945, 6961, 7821, 7841, 7861, 7931G, 7940, 7940G, 7941, 7941G, 7942, 7942G, 7945, 7945G, 7960, 7960G, 7961, 7961G, 7962, 7962G, 7965, 7965G, 7970, 7970G, 7971, 7971G, 7975, 7975G, 8811, 8841, 8851, 8861, 8941, 8945, 8961, 9951, 9971

Also works with these Plantronics Amplifier:
M10, M12 , M22 , MX10

Specifications:

• (1) 2.5mm TRS female jack
• (1) 4P4C RJ9/RJ10 male plug
• Use your existing 2.5mm TRS headset (must have a 2.5mm TRS Plug, NOT 3.5mm common in most audio peripherals)
• Avoid having to purchase an expensive Cisco headset
• Length: 1ft

CablesOnline Part Number: IP-CS12